This invention relates to an apparatus for measuring the electric field intensity of an electric wave, such as a signal wave, a noise wave or the like, and more particularly to an electric field measuring apparatus which is simple in manipulation.
In a conventional electric field intensity measuring apparatus, the input side of a receiver is connected first to the side of an antenna, the oscillation frequency of a local oscillator is manually controlled to select an electric wave to be measured, the attenuation of a high-frequency attenuator and the gain of an intermediate-frequency variable gain amplifier are adjusted so that the received detected output of the selected electric wave is indicated in a predetermined proper value by an indicator, and the set values of these level adjusters are read out. Then, the receiver input side is switched from the antenna to the output side of a reference oscillator and, at the same time, the reference oscillator is caused to oscillate at the same frequency as that of the electric wave to be measured. The oscillator output is predetermined. This oscillator output is similarly level-adjusted to cause the indicator to provide an indication of the predetermined value of the oscillator output, and the set values of the level adjusters at this time are read out. Further, a coefficient for compensating for the frequency characteristic of the antenna is read out, for example, from a graph relating such coefficients to the frequency of the electric wave to be measured. Based on this coefficient, the abovesaid two level set values, and the output from the reference oscillator, the electric field intensity of the electric wave to be measured is obtained.
As described above, the conventional electric field intensity measuring apparatus is troublesome in manipulation. Moreover, since the coefficient for compensating for the frequency characteristic of the antenna differs with the various frequencies of electric waves to be measured, compensating coefficients are prepared in the form of a graph and selectively read out therefrom for each measurement of the electric field intensity.
There has also been proposed a measuring equipment designed for measuring the electric field intensities of both a continuous wave and a noise wave. The measurement of the noise wave is generally rated, and a detector is set to have a quasi-peak value detecting mode of operation. For measurement of the continuous wave, as opposed to a noise wave, the detector is switched to a mean value detecting mode of operation to detect an envelope of an intermediate-frequency carrier. In the case of the quasi-peak value detection, the envelope is converted to direct current form, that is, averaged to some extent, so that when the detector is changed over to the quasi-peak value detecting mode, the detected output decreases as compared with that in the case of the mean value detecting mode. Accordingly, when the detector is switched to the mean value detection mode from the quasi-peak value detection mode, in which the detected output has a reference value, that is, the indicator indicates its maximum scale value, the mean value detected output increases, resulting in the indicator "scaling over". Therefore, in order to obtain the detected output at a predetermined reference level, it is necessary that each stage preceding the detector be used at a level lower than a maximum level permissible for that stage.
In the quasi-peak value detection mode, the detected output is smaller than that in the mean value detection mode, for example, by about 40 dB. As a result of this, the measuring range, i.e. the dynamic range of measurement decreases approximately 40 dB as compared with that in the case of no noise wave being measured. In other words, it is impossible to make full use of the permissible level range of each stage preceding the detector.
It is an object of this invention to provide an electric field intensity measuring apparatus which is very simple in manipulation but capable of accurate measurement.
It is another object of this invention to provide an electric field intensity measuring apparatus which enables the full use of allowed levels of stages preceding the detector to the maximum extent possible in the measurement of the field intensities of both of a noise wave and a continuous wave, and which provides a wide dynamic range of measurement.